For certain wireless networking applications, it is desirable if not essential for the network to have all of the following properties: First, it should be self-forming or “ad-hoc” in nature. That is, the formation of the network does not depend upon the presence of a pre-determined central coordinator. Second, it should be able to accommodate relatively rapid changes in network configuration, including changes in the number and location of the devices participating in the network, and changes in the channel conditions experienced by communication devices. Third, it should be able to accommodate an extended network system where the population of devices that are able to communicate wirelessly, either directly, or indirectly via devices that also act as repeaters, may be spread over a relatively large geographic area. Fourth, it should be able to provide robust Quality of Service through the use of time reservations or “slots” during which one device or a limited number of devices are allowed to transmit. Fifth, it should provide good power management qualities, such that there are mechanisms which allow devices minimize active time and to transition in and out of reduced power “sleep” states while still maintaining the ability to communication.
Unfortunately, wireless networks are not this robust. Instead a wireless network requires a central coordinator to establish a timing scheme. Wireless networks typically are organized into “cells”. Each cell is managed by a central coordinator. Devices within range of a given coordinating device may join the cell and participate in the network. Central cell coordinators transmit special frames known as “beacons” at precise intervals. Beacons typically provide the following functions: announce the existence of the network; indicate the network's capabilities; provide a timing mark for network synchronization; provide timing information for when different network access methods are available, including reserved “slots” of time for use by a single station or a limited number of stations; and provide timing information and other information which allows devices to determine when they may enter and exit reduced power management states.
The time from one beacon to the next is sometimes referred to as a “superframe”. The central coordinator maintains superframe timing, including the superframe interval (or conversely, the superframe repetition rate) and the superframe phase (superframe start time). Specific intervals or “slots” are established relative to beacon transmission, or more precisely, relative to the start of the superframe. Devices that are synchronized to the central coordinator and that have one or more reserved slots may transmit at the appropriate time during the superframe, even if some beacons are not properly received
To summarize, with current wireless networks, frames (i.e. “beacons”) that provide an indication of the position in time of the superframe are sent only by central coordinators, and are sent either precisely at the start of the superframe, or as soon network conditions permit after the start of the superframe. The superframe forms a time basis for managing and scheduling network activity. However, this type approach does not provide the desirable properties described above. Instead, a need exists for a system of coordinating a wireless network that does not have a central coordinator.